The present invention relates to the isomerization of an alkylation product, formed by the alkylation of phenol with an olefin in the presence of a super acid catalyst containing Bronsted acid functionality. The term xe2x80x9cisomerization, as used herein, is meant to indicate the change in overall isomer distribution of an alkylated phenol composition by intra- and/or intermolecular mechanism(s). Such a product normally contains a certain level of undesired mono, di and tri-substituted ortho-alkylphenols (or mixture thereof). It is desired to reduce the level of such ortho-substituted alkylphenols, in such an alkylation product since such ortho-substituted components are significantly less reactive in any later desired phosphorylation reaction using the alkylated phenol and also may be deemed by some persons to be more undesired from a toxicological viewpoint. The phosphorylation of such materials is a well-known reaction and involves treating them with a phosphorylating reagent (such as phosphorus oxytrichloride) at moderately elevated temperature (such as about 100xc2x0 C. to about 200xc2x0 C.), preferably in the presence of a Friedel-Crafts catalyst.
One prior art reference that relates to the use of trifluoromethane sulfonic acid (also termed xe2x80x9ctriflic acidxe2x80x9d) as the catalyst to achieve the general type of isomerization that forms the subject matter of the present invention is U.S. Pat. No. 4,103,096 to S. L. Giolito et al., which is incorporated herein in its entirety. This patent illustrates, in general terms, one conventional way in which this isomerization reaction has been practiced.
While the use of trifluoromethane sulfonic acid catalyst, as just described, has been utilized commercially, its use is attendant with certain disadvantages. The use of relatively high levels-of this catalyst (e.g., 800 to 1000 ppm) may be needed for the desired level of isomerization to take place, and the use of such levels of this acid can cause unacceptable color change in the product of the reaction. Trifluoromethane sulfonic acid is a strong acid that can cause corrosion damage in the process equipment that is used. This catalyst cannot be recovered and hence the catalyst costs are not trivial. Finally, the isomerization reaction using this acid is rather slow (e.g., 40 to 60 hours) in order to reach the target isomer distribution.
Other methods which have been proposed for practicing analogous isomerization reactions are shown in the following patent and literature references: Japanese Patent Publication No. 45-30091/1970; U.S. Pat. No. 3,014,079; and J. Org. Chem., 38, 1929 (1973).
The present invention relates to the isomerization of the previously described alkylation product to reduce the level of ortho-substituted product therein using a new class of catalyst: a solid acid catalyst.
As previously described, the present invention is an isomerization reaction which relies upon the use of a novel class of catalyst for that particular type of reaction. In general terms, the alkylation product which is treated herein will comprise a mixture of alkylated phenols: from about 10% to about 30%, by weight of the ortho-substituted alkylated phenols; from about 0% to about 5%, by weight of meta-substituted alkylated phenols; from about 5% to about 15%, by weight of para-substituted alkylated phenols; from 2% to 10% by weight 2,6-dialkylated phenol; and from 1% to 5% tri-alkylated phenol. The present invention relies upon a solid acid catalyst, as will be described below in further detail, to lower the amount of such ortho-substituted species so that the final product preferably has the following composition: from about 10% to about 20%, by weight of ortho-substituted alkylated phenols; from about 5% to about 20%, by weight of meta-substituted alkylated phenols; from about 10% to about 30%, by weight of para-substituted alkylated phenols; and from about 0.5% to 3% 2,6-di-isopropyl phenol. The present invention is useful, for example, in the isomerization of mono-alkylsubstituted phenols, such as monoisopropylphenol, of di-alkylsubstituted phenols, such as 2,6-diisopropylphenol, or mixtures containing such alkylated species. The alkyl group or groups on the phenols which are treated will generally have from about two to about twelve carbon atoms therein, preferably three or four, such as exemplified by the isopropyl and tert-butyl groups.
The general type of isomerization reaction is shown in the aforementioned Giolito et al. patent in which the catalyst is employed at a level of from about 0.01% to about 5%, by weight of the alkylphenol, preferably from about 300 to 3000 ppm, and the reaction temperature for the isomerization reaction will be in the range of from about 170xc2x0 C. to the reflux temperature of the alkylphenol-containing composition which is treated preferably from about 100xc2x0 C. to about 250xc2x0 C. The reaction can be performed advantageously at atmospheric pressure or elevated pressure (e.g., up to about 500 psig). The Present process is practiced in the absence of an alkylating agent, such as an olefin.
In accordance with the present invention, a variety of solid acid catalyst types, which are well known to the person of ordinary skill in the art for other chemical reactions, can be used herein. Included as general types of such solid acid catalysts are the H-form zeolites, the supported sulfonic acids, and the heteropoly acids.
Representative examples of H-form zeolites, which form a well-known class of commercially available materials, which find preferred utility in the present invention are the Y-type zeolites and the beta zeolites. Such materials contain Bronsted acid functionality that is needed in the process of the present invention. The ZSM type and mordenite class of zeolites also can be used, but they have been found to have somewhat lower activity. The zeolites that are used herein preferably have a silica/alumina ratio of from about 5 to about 100, most preferably from about 5 to about 80.
Representative supported sulfur acid catalysts include the sulfonic acid catalysts, sulfated zirconia (commercially available, for example, from MEI Chemicals) and the perfluorinated ionic exchange polymers that are available from DuPont under the trademark NAFION. The latter type of material is described at Col. 2, line 24 to Col. 3, line 47 of U.S. Pat. No. 5,001,281 to S. M. Li, which description is incorporated herein by reference.
A supported heteropoly acid catalyst can also be used in connection with the present invention. The description of these materials that appears at Col. 2, line 46 to Col. 5, line 24, for example, of U.S. Pat. No., 5,300,703 of J. F. Knifton, is incorporated herein as describing such known catalytic materials. The Knifton patent deals with the use of such heteropoly acid materials in the synthesis, rather than in the isomerization, of an alkylphenol composition.
The present invention""s catalyst selection has a number of advantages, as compared to the use of the liquid catalyst trifluoromethane sulfonic acid previously described. The use of a solid catalyst precludes the possibility that it will become lost by dissolution in the liquid reaction media. There is also no need to use the more difficult means needed to separate a liquid catalyst from a liquid reaction product. The solid acid catalyst is more amenable to a continuous reaction process as compared to the use of a liquid catalyst. The solid catalyst used herein is more easy to regenerate than the trifluoromethane sulfonic acid catalyst that has been previously described. Finally, the solid acid catalysts that are described for use herein have been found to generally yield a product having lower color characteristics than were achieved in many cases using the trifluoromethane sulfonic acid catalyst of the prior art.
When a zeolite is selected as the solid acid catalyst for use herein, it has been found that certain novel compositions can be obtained. Such compositions comprise a mixed alkylphenols wherein the ratio of ortho- to meta- and para- isomers is no more than about 1.0, the amount of 2,6-dialkyl phenol is no more than about 4.0%, by weight of the entire composition, and the amount of trialkyl phenol is from about 4% to about 75% (preferably about 4% to about 15%), by weight of the entire composition.
The present process can be practiced using a variety of reaction schemes. For example, it is possible to implement the present invention using batch reaction, fixed bed reaction, or reactive distillation reaction techniques, or a combination of those techniques.
In those cases where a zeolite catalyst is employed, it has been found that such catalysts undergo varying levels of deactivation, due to the formation of carbonaceous species that block the active sites. Such a catalyst can be easily regenerated using known regeneration procedures. For example, a controlled burnout of the carbonaceous species can be achieved using air/nitrogen mixtures that are lean in oxygen at temperatures of from about 200xc2x0 C. to about 500xc2x0 C.
The invention will be further illustrated in the following non-limiting Examples.